1. Field of the Invention
The present invention relates to a sheet discharging apparatus for discharging a sheet, and a sheet treating apparatus and an image forming apparatus each provided with the sheet discharging apparatus in its sheet discharging portion. Particularly, the present invention relates to a sheet treating apparatus and an image forming apparatus each capable of maintaining its charge elimination effect for a long time of period.
2. Related Background Art
In recent years, as an option for an image forming apparatus such as an electrophotographical copying machine and a laser beam printer, there have been developed sheet treating apparatuses such as a sorter for sorting image-formed sheets. Such a kind of sheet treating apparatus is made capable of executing at least one treatment of sheets, such as sorting, stapling or binding, and alignment.
In a sheet treating apparatus provided with a stapler for performing stapling with a needle, the stapling operation is performed on sheets conveyed into a main body of the sheet treating apparatus, after each of the sheet is passed through a conveyance path formed in the main body, and stacked on a tray for post-treatment.
The sheet treating apparatus for stapling a stack of sheets is adapted to stack sheets on the tray for post-treatment, and perform stapling of the sheets at a location, or at plural locations (normally at two locations) by moving the stapler serving as a stapling unit. During the stapling operation, it is impossible to stack sheets for next job on the tray for post-treatment. Accordingly, it is necessary to set an interval between sheets of different job units on which the stapling operation is to be executed.
However, in the event that the interval is set between the sheets, productivity lowers. In other words, the number of sheets capable of being treated per unit time decreases. As a sheet treating apparatus for preventing such decrease in the productivity, there has been proposed a sheet treating apparatus as illustrated in FIG. 9 (see Japanese Patent Application Laid-Open No. 9-48545, for example).
In a conventional sheet treating apparatus 10 illustrated in FIG. 9, a buffer roller path 14 is provided halfway in a conveyance path 12 for conveying a sheet to a post-treatment tray 11. In the buffer roller path 14, the sheet is wound on a rotary buffer roller 13, and conveyance of the sheet to the post-treatment tray 11 is thus put under a stand-by condition. Further, in the sheet treating apparatus 10 illustrated in FIG. 9, in the event that sheets stacked in the post-treatment tray 11 are to be treated, these sheets are treated by a stapler or the like after their ends are aligned by a stopper. In the sheet treating apparatus 10 illustrated in FIG. 9, accordingly, sheets stacked in the post-treatment tray 11 after passed through the buffer roller path 14 or a straight path 20 are sandwiched between upper and lower rollers 18a and 18b provided in a bracket 19 rotatable about an axis 21, and are brought into contact with the stopper by rotations of these rollers. The thus-treated sheets are discharged into and stacked in a stack tray 23 by reverse rotations of the upper and lower rollers 18a and 18b. 
Thus, in the conventional sheet discharging apparatus as illustrated in FIG. 9, where sheets are to be treated by the stapler or the like, the sheets are reciprocally conveyed in such a manner that they are conveyed leftward and discharged after they are once conveyed rightward.
In the conventional sheet treating apparatus 10 having the above-discussed construction, sheets conveyed from a pair of sheet discharging rollers 17 in a main body 16 of an image forming apparatus 15 are stored in the buffer roller path 14, and a stack of these sheets stored in the buffer roller path 14 is conveyed to the post-treatment tray 11, after stapling of a stack of preceding sheets on the post-treatment tray 11, for example, is finished, and the stack of sheets is discharged from the post-treatment tray 11 by pinching and rotating operation of the upper and lower rollers 18a and 18b in a pair of swinging rollers (oscillation rollers) 18. Therefore, conveyance intervals between sheets during the stapling operation need not be widened, and the decrease in the productivity can be hence prevented.
Sheets discharged to the stack tray 23 by the pair of swinging rollers 18 serving as the sheet discharging apparatus 19 are likely to be brought into close contact with each other due to static electricity generated by sliding contact with the pair of swinging rollers 18, and hence there is a possibility that it is difficult for a user to separate the sheets from each other. Further, in the event that discharged sheets are stacked under a curling condition due to the static electricity, there is a possibility that the sheet falls from the stack tray 23 by being pushed by its following sheet.
In the sheet treating apparatus 10, therefore, a charge eliminating member 24 is provided in the bracket 19 for holding the upper roller 18a of the pair of swinging rollers 18. The charge eliminating member 24 is brought into contact with a sheet when the bracket 19 is rotated in a counterclockwise direction about the axis 21 to sandwich the sheet between the upper and lower rollers 18a and 18b. The static electricity stored in the sheet is hence grounded.
However, the charge eliminating member 24 provided in the sheet discharging apparatus of the conventional sheet discharging apparatus 10 is generally an elastic thin metal plate, or an elastic piece, such as an elastic print board, with a metal foil bonded thereto.
Accordingly, the charge eliminating member cannot securely remove the static electricity since only its tip portion having a small area is brought into contact with the sheet. If its contact area or its contact pressure is increased to surely remove the static electricity, there is a fear that the charge eliminating member hurts the sheet.
With the conventional charge eliminating member, therefore, it is difficult that the contact area or the contact pressure is so adjusted as to surely remove the static electricity without hurting the sheet.
Further, where the sheet discharging apparatus is provided in the above-discussed sheet treating apparatus, the charge eliminating member is reciprocally flexed each time the sheet is discharged by the above-discussed reciprocal movement of the sheet. As its result, the charge eliminating member is liable to deform or lose its elasticity, and hence there is a fear that the charge eliminating member cannot be securely brought into contact with the sheet, and the charge elimination effect lowers.